A vessel

ABSTRACT

A vessel (1) comprises a hull (2) including a bow (3) and a stern (4) and has a length-to-beam ratio which is smaller than 10:1, preferably smaller than 5:1. The hull (2) has a vertical centre plane (CP) extending in a direction from the bow (3) to the stern (4). At each side of the centre plane (CP) the vessel (1) has at least two azimuth thrusters (6) including respective propellers (6a), which azimuth thrusters (6) are located next to each other in transverse direction of the centre plane (CP). Each azimuth thruster (6) drivably coupled to its own prime mover (7).

The present invention relates to a vessel comprising a hull including a bow and a stern and having a length-to-beam ratio which is smaller than 10:1, preferably smaller than 5:1, wherein the hull has a vertical centre plane extending in a direction from the bow to the stern.

Such a vessel is known, for example in the form of a tug boat of which the length-to-beam ratio is about 3:1. A typical known tug boat has two azimuth thrusters for propelling and manoeuvring the tug boat, which azimuth thrusters are located at either side of the centre plane. The azimuth thrusters are drivably coupled to respective diesel engines and can be operated by a helmsman, for example by means of respective joysticks.

An object of the invention is to provide a highly manoeuvrable vessel.

This object is achieved with the vessel according to the invention, wherein at each side of the centre plane the vessel has at least two azimuth thrusters including respective propellers, which azimuth thrusters are located next to each other in transverse direction of the centre plane and wherein each azimuth thruster is drivably coupled to its own prime mover. Hence, a row of at least four azimuth thrusters extends in transverse direction of the hull. In practice, the same number of azimuth thrusters will be located at both sides of the centre plane.

Due to the relatively small length-to-beam ratio the relatively wide beam provides the possibility to apply a plurality of azimuth thrusters at each side of the centre plane. For achieving a similar power level, an increasing number of azimuth thrusters may have decreasing propeller diameters of the individual azimuth thrusters. Consequently, the total height of the series of azimuth thrusters can be kept relatively small.

The application of relatively small azimuth thrusters also provides the opportunity to apply relatively small cooperating prime movers. An advantage of relatively small azimuth thrusters and prime movers is that their response time is relatively short, which leads to improved manoeuvrability of the vessel.

In a practical embodiment the azimuth thrusters are aligned in transverse direction of the centre plane.

Distances between centrelines of the propellers of each two neighbouring azimuth thrusters may be the same in order to achieve a symmetric arrangement. The distance between centrelines of the propellers of the neighbouring azimuth thrusters which are located at either side of the central plane, i.e. the two azimuth thrusters which are located closest to the central plane, may be different from the distance between the centrelines of the propellers of each two neighbouring azimuth thrusters at each side of the centre plane.

In a particular embodiment the propellers of the at least two azimuth thrusters have different diameters. The propeller of one of the at least two azimuth thrusters which is located at a larger distance from the centre plane than the other one of the at least two azimuth thrusters may have a larger diameter than the propeller of the other one of the at least two azimuth thrusters.

The azimuth thrusters may be located at the bow or at the stern.

At least one of the prime movers may be an internal combustion engine. The internal combustion engine may be a diesel engine having a maximum speed above 1000 rpm. Such a diesel engines may be known as a high-speed diesel engine. If the desired power per individual azimuth thruster is relatively large such that a low-speed diesel engine must be applied, it is in the spirit of the present invention preferred to apply a higher number of relatively small azimuth thrusters including high-speed diesel engines instead of applying a smaller number of relatively large azimuth thrusters including low-speed diesel engines.

The at least two azimuth thrusters and their prime movers may be functionally coupled to a common controller for operating the at least two azimuth thrusters simultaneously. The common controller may be a joystick such that an operator can operate two joysticks, one for simultaneously controlling the at least two azimuth thrusters including their prime movers at one side of the centre plane and one for simultaneously controlling the at least two azimuth thrusters including their prime movers at the other side of the centre plane.

In a particular embodiment at each side of the centre plane a skeg is mounted to a lower side of the hull, which skeg extends in longitudinal direction of the hull, for example from the bow to about halfway the hull. In this embodiment the vessel has at least two skegs which may have a relatively small height, which reduces draught of the vessel, improves seakeeping behaviour and facilitates easy docking. Furthermore, at least two skegs improve course stability and manoeuvrability and allows relatively large steering forces during escorting a large vessel.

The skeg may be located at a horizontal position between axes of rotation of the respective propellers of the at least two azimuth thrusters as seen in a direction from the stern to the bow.

Furthermore, the maximum height of the skeg may be smaller than the diameter or 1.5 times the diameter of each of the propellers of the respective azimuth thrusters, or even smaller than 80% thereof.

The vessel may be a tug boat.

The invention will hereafter be elucidated with reference to very schematic drawings showing embodiments of the invention by way of example.

FIG. 1 is a side view of an embodiment of a vessel according to the invention.

FIG. 2 is a plan view of a part of the vessel as shown in FIG. 1 on a larger scale.

FIG. 3 is a rear view of the vessel as shown in FIG. 1 on a larger scale.

FIG. 4 is a similar view as FIG. 3 , but showing an alternative embodiment.

FIGS. 1-3 show an embodiment of a vessel according to the invention. The vessel is a tug boat 1, which has a hull 2 including a bow 3 and a stern 4. Such a tug boat 1 is typically used as an escort tug, anchor handling tug, salvage tug, oil recovery vessel, safety stand-by vessel or as ship handling tug near offshore terminals and FPSOs (Floating Production Storage and Offloading vessels). The tug boat 1 may be used for assisting large ships which are much larger than the tug boat 1. The tug boat 1 may be connected to the large ship by a towing cable for towing the large ship in a specific direction or the tug boat 1 is manoeuvred against the large ship in order to be able to push it in a certain direction.

The hull 2 of the tug boat 1 as shown in FIGS. 1-3 has a length of about 50 m and a beam of about 16 m, hence a length-to-beam ratio of about 3. The hull 2 has a vertical centre plane CP which extends in a direction from the bow 3 to the stern 4, see FIGS. 2 and 3 . A central skeg 5 is mounted to a lower side of the hull 2. The central skeg 5 extends in longitudinal direction of the hull 2 from the bow 3 to about halfway the hull 2 at the centre plane CP.

The tug boat 1 is provided with a series of four azimuth thrusters 6, which are arranged in an aligned row that extends in transverse direction of the centre plane CP. The azimuth thrusters 6 have respective propellers 6 a which are located below the hull 2, in this case at the stern 4. In an alternative embodiment the azimuth thrusters 6 may be located at the bow 3 or elsewhere in between.

The application of an azimuth thruster for propelling a vessel is well-known, for example in ASD (azimuth-stern-drive) tug boats. The entire propulsion unit can turn in the horizontal plane and thrust can be produced in any desired direction.

In the embodiment as shown in FIGS. 1-3 at each side of the centre plane two azimuth thrusters 6 are located next to each other in transverse direction of the centre plane CP and the azimuth thrusters 6 are drivably coupled to respective prime movers in the form of high-speed diesel engines 7 via respective propeller shafts 8. The high-speed diesel engines 7 are located within the hull 2 below a deck 9. The high-speed diesel engines 7 provide a fast response when increased thrust is desired.

FIG. 3 shows that the propellers 6 a of the outer two azimuth thrusters 6 have larger diameters than the propellers 6 a of the inner two azimuth thrusters 6.

The pair of azimuth thrusters 6 and their prime movers 7 at one side of the centre plane CP can be operated simultaneously by a first joystick and the pair of azimuth thrusters 6 and their prime movers 7 at the other side of the centre plane CP can be operated simultaneously by a second joystick.

FIG. 4 shows an alternative embodiment, which distinguishes from the embodiment as shown in FIG. 3 in that two skegs 5 a, 5 b are mounted to a lower side of the hull 2. The skegs 5 extend in longitudinal direction of the hull 2 from the bow 3 to about halfway the hull 2 at a distance from the centre plane CP. As seen from behind of the hull 2, each of the skegs 5 a, 5 b is located at a horizontal position between axes of rotation of the propellers 6 a of the neighbouring azimuth thrusters 6. Due to the application of two skegs 5 a, 5 b their dimensions in vertical direction are relatively small, which creates a relatively small draught. Hence, the combination of at least two relatively small azimuth thrusters 6 and at least one skeg 5 a, 5 b at each side of the centre plane CP allows a small draught and facilitates docking, for example. The height of each of the skegs 5 a, 5 b may vary along its longitudinal direction. The maximum height may be smaller than the diameter or 1.5 times the diameter of each of the propellers 6 a.

The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents. 

1. A vessel comprising a hull including a bow and a stern and having a length-to-beam ratio which is smaller than 10:1, wherein the hull has a vertical center plane extending in a direction from the bow to the stern, at each side of the center plane the vessel has at least two azimuth thrusters each including respective propellers, which azimuth thrusters are located next to each other in a transverse direction of relative to the center plane (CP) and each azimuth thruster is coupled to its own prime mover in a manner whereby each azimuth thruster Is capable of being driven by the respective prime mover.
 2. The vessel according to claim 1, wherein the azimuth thrusters are aligned in transverse direction relative to the center plane.
 3. The vessel according to claim 1, wherein distances between centerlines of the propellers of each two of the neighbouring azimuth thrusters are the same.
 4. The vessel according to claim 1, wherein the propellers of the at least two azimuth thrusters have different diameters.
 5. The vessel according to claim 4, wherein the propeller of one of the at least two azimuth thrusters which is located at a larger distance from the center plane than another one of the at least two azimuth thrusters has a larger diameter than the propeller of the another one of the at least two azimuth thrusters.
 6. The vessel according to claim 1, wherein the azimuth thrusters are located at the bow or at the stern.
 7. The vessel according to claim 1, wherein at least one of the prime movers is an internal combustion engine.
 8. The vessel according to claim 7, wherein the internal combustion engine is a diesel engine.
 9. The vessel according to claim 8, wherein the diesel engine has a maximum speed above 1000 rpm.
 10. The vessel according to claim 1, wherein the at least two azimuth thrusters and their prime movers are functionally coupled to a common controller for operating the at least two azimuth thrusters simultaneously.
 11. The vessel according to claim 10, wherein the common controller for each of the at least two azimuth thrusters and their prime movers is a joystick configured such that an operator can operate two joysticks, the joystick for simultaneously controlling the at least two azimuth thrusters including their prime movers at one side of the center plane and the second joystick for simultaneously controlling the at least two azimuth thrusters including their prime movers at the other side of the center plane.
 12. The vessel according to claim 1 wherein at each side of the center plane a skeg is mounted to a lower side of the hull, which skeg extends in longitudinal direction of the hull.
 13. The vessel according to claim 12, wherein the skeg is located at a horizontal position between axes of rotation of the respective propellers of the at least two azimuth thrusters, as seen in a direction from the stern to the bow.
 14. The vessel according to claim 12, wherein a maximum height of the skeg is smaller than a diameter or of each of the propellers of the respective azimuth thrusters.
 15. The vessel according to claim 1, wherein the vessel is a tug boat.
 16. The vessel according to claim 1, wherein the length-to-beam ratio is smaller than 5:1.
 17. The vessel according to claim 14, wherein maximum height of the skeg is smaller than 1.5 times the diameter of each of the propellers of the respective azimuth thrusters.
 18. The vessel according to claim 2, wherein distances between centerlines of the propellers of each two of the neighbouring azimuth thrusters are the same.
 19. The vessel according to claim 2, wherein the propellers of the at least two azimuth thrusters have different diameters.
 20. The vessel according to claim 19, wherein the propeller of one of the at least two azimuth thrusters which is located at a larger distance from the center plane than another one of the at least two azimuth thrusters has a larger diameter than the propeller of the another one of the at least two azimuth thrusters. 